// GenericsNote: Converted.
/*
 *  Copyright 2001-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.apache.commons.collections15.comparators;

import java.io.Serializable;
import java.util.Comparator;

/**
 * A Comparator that will compare nulls to be either lower or higher than
 * other objects.
 *
 * @author Matt Hall, John Watkinson, Michael A. Smith
 * @version $Revision: 1.1 $ $Date: 2005/10/11 17:05:20 $
 * @since Commons Collections 2.0
 */
public class NullComparator <T> implements Comparator<T>, Serializable {

    /**
     * Serialization version.
     */
    private static final long serialVersionUID = -5820772575483504339L;

    /**
     * The comparator to use when comparing two non-<code>null</code> objects.
     */
    private Comparator<T> nonNullComparator;

    /**
     * Specifies whether a <code>null</code> are compared as higher than
     * non-<code>null</code> objects.
     */
    private boolean nullsAreHigh;

    /**
     * Construct an instance that sorts <code>null</code> higher than any
     * non-<code>null</code> object it is compared with.  When comparing two
     * non-<code>null</code> objects, the specified {@link Comparator} is
     * used.
     *
     * @param nonNullComparator the comparator to use when comparing two
     *                          non-<code>null</code> objects.  This argument cannot be
     *                          <code>null</code>
     * @throws NullPointerException if <code>nonNullComparator</code> is
     *                              <code>null</code>
     */
    public NullComparator(Comparator<T> nonNullComparator) {
        this(nonNullComparator, true);
    }

    /**
     * Construct an instance that sorts <code>null</code> higher or lower than
     * any non-<code>null</code> object it is compared with.  When comparing
     * two non-<code>null</code> objects, the specified {@link Comparator} is
     * used.
     *
     * @param nonNullComparator the comparator to use when comparing two
     *                          non-<code>null</code> objects. This argument cannot be
     *                          <code>null</code>
     * @param nullsAreHigh      a <code>true</code> value indicates that
     *                          <code>null</code> should be compared as higher than a
     *                          non-<code>null</code> object.  A <code>false</code> value indicates
     *                          that <code>null</code> should be compared as lower than a
     *                          non-<code>null</code> object.
     * @throws NullPointerException if <code>nonNullComparator</code> is
     *                              <code>null</code>
     */
    public NullComparator(Comparator<T> nonNullComparator, boolean nullsAreHigh) {
        this.nonNullComparator = nonNullComparator;
        this.nullsAreHigh = nullsAreHigh;

        if (nonNullComparator == null) {
            throw new NullPointerException("null nonNullComparator");
        }
    }

    //-----------------------------------------------------------------------
    /**
     * Perform a comparison between two objects.  If both objects are
     * <code>null</code>, a <code>0</code> value is returned.  If one object
     * is <code>null</code> and the other is not, the result is determined on
     * whether the Comparator was constructed to have nulls as higher or lower
     * than other objects.  If neither object is <code>null</code>, an
     * underlying comparator specified in the constructor (or the default) is
     * used to compare the non-<code>null</code> objects.
     *
     * @param o1 the first object to compare
     * @param o2 the object to compare it to.
     * @return <code>-1</code> if <code>o1</code> is "lower" than (less than,
     *         before, etc.) <code>o2</code>; <code>1</code> if <code>o1</code> is
     *         "higher" than (greater than, after, etc.) <code>o2</code>; or
     *         <code>0</code> if <code>o1</code> and <code>o2</code> are equal.
     */
    public int compare(T o1, T o2) {
        if (o1 == o2) {
            return 0;
        }
        if (o1 == null) {
            return (this.nullsAreHigh ? 1 : -1);
        }
        if (o2 == null) {
            return (this.nullsAreHigh ? -1 : 1);
        }
        return this.nonNullComparator.compare(o1, o2);
    }

    //-----------------------------------------------------------------------
    /**
     * Implement a hash code for this comparator that is consistent with
     * {@link #equals(Object)}.
     *
     * @return a hash code for this comparator.
     */
    public int hashCode() {
        return (nullsAreHigh ? -1 : 1) * nonNullComparator.hashCode();
    }

    /**
     * Determines whether the specified object represents a comparator that is
     * equal to this comparator.
     *
     * @param obj the object to compare this comparator with.
     * @return <code>true</code> if the specified object is a NullComparator
     *         with equivalent <code>null</code> comparison behavior
     *         (i.e. <code>null</code> high or low) and with equivalent underlying
     *         non-<code>null</code> object comparators.
     */
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (obj == this) {
            return true;
        }
        if (!obj.getClass().equals(this.getClass())) {
            return false;
        }

        NullComparator other = (NullComparator) obj;

        return ((this.nullsAreHigh == other.nullsAreHigh) && (this.nonNullComparator.equals(other.nonNullComparator)));
    }

}
